1. Field of the Invention
The present invention relates to electroluminescent lamps, and more particularly to a method for manufacturing water proof electroluminescent lamps which are suitable for many low-cost consumer applications.
2. Description of the Prior Art
Conventional electroluminescent (EL) lamp manufacturing techniques may be divided into two basic processes. The first is a screen printing process in which the lamp is constructed layer by layer. More particularly, the lamp is constructed using costly electroluminescent inks, clear conductive indium tin oxide (ITO) transparent films, conductive inks compounded with a high volume of metallic silver and a water repellent electrical insulating coating containing an ultraviolet light-activated polymer.
The screen printing process allows intricate graphics effects to be created using relatively simple manufacturing processes. However, screen printed EL lamps having high luminance or superior electrical characteristics tend to be costly to manufacture. Typical manufacturing costs in high volume applications range from eight to thirteen cents per square inch, while minimal quality and performance standards result in savings of less than two cents per square inch.
The second process is the continuous lamination method. In this process, a first film which supports a foil is passed below a metering roller or blade which applies an insulating layer of ink. A second transparent film that has been sputter coated with clear conductive ITO is similarly passed below a roller or blade, which applies a layer of phosphor ink. In order to achieve a uniform light output and electrical characteristics, the thickness of the insulating and phosphor layers must be precisely controlled, along with the phosphor grain dispersion in the phosphor layer. Thus, the continuous lamination method requires very tight control over ink rheology.
Once the ink layers have been dried and inspected for defective areas, the first and second films are laminated together to form a lamp core. The film lamination requires heat and/or pressure which must be tightly controlled so that the light and electrical characteristics of the finished lamp are not affected. Additionally, since the phosphor layer is sensitive to water contamination, the finished lamp is cut into the desired size and shape, electrically terminated and encapsulated within a water impervious lamination film (such as Allied Signal's "ACLAR" CTFE).
The continuous lamination method produces foil EL lamps, which are high performance, high priced lamps typically unsuitable for graphics or other price-sensitive applications. Foil EL lamps are also thicker and mechanically less flexible than screen printed EL lamps. The typical cost of foil sensitive lamps is greater than thirty cents per square inch, and the lamps are typically used in military, aircraft and high-end industrial applications.
Accordingly, there is a need for a method for manufacturing low-cost EL lamps which can be applied to both graphics and price-sensitive consumer applications.